Fig. 1: The relationship between the adsorption isotherm and the adsorbent structure.

a Type I adsorption isotherm and rigid microporous materials. b S-shaped adsorption isotherm and flexible porous materials. c Negative gas adsorption isotherm associated with structural deformation and pore contraction of adsorbents. d, e Negative pressure inflexion adsorption isotherm and structural changes of the adsorbent with increasing gas pressure.